If the Big Bang happened again

[gib65]

I ask this question solely for the purpose of testing my understanding of quantum mechanics. I want to ask, if the universe was to start all over again with the Big Bang, and assuming all conditions were exactly as they were 14 billion years ago, would we or would we not get exactly the same things we see on Earth today? Would I still be a web developer? Would I still have married the woman I'm married to? Would I still be here at my computer, typing these very words?

 

From what I understand, the indeterminacy of the measurable properties of really small things means that the results predicted by classical mechanics are not met 100% of the time.

 

So for example, one of the classic text book exercises ask to calculate the position of a boat traveling against the current in so much time if it started from a given position. There is one and only on answer to this question. But if you were to ask a similar question about the position of an electron, you'd have to take quantum mechanics into consideration, and thereby you would only be able to give a probabilistic answer. The electron would be in position X give or take a radius of r. Right?

 

Of course, r is infinitesimally small relative to the everyday scale of human events, so there wouldn't be any reason to suppose that such deviations from the prediction of classical mechanics would have global consequences. So if I were to pose the above question with respect to my waking up this morning, asking "If I were to repeat waking up this morning with all conditions setup exactly as they were, would I still be doing exactly what I'm doing now?", I could reasonably say "yes, I would."

 

But if we were to take this scenario all the way back 14 billion years ago to the Big Bang, what would be the answer then? 14 billion years is a lot of time, so even though the aberrations of quantum mechanics are extremely miniscule, given this much time, with aberration after aberration piling up upon each other, the effects might actually become noticeable. Would I still be sitting here typing these words on my keyboard?

[Klaynos]

If everything was exactly perfectly the same, (as it's a chaotic system even a small deviation can cause MASSIVE differences to final conditions) then the answer depends who you ask, there's a bit of a debate going on atm.

 

*searches for new scientist article*

 

http://www.newscientist.com/article/mg19025504.000.html

[[Tycho?]]

I dont think anyone can give a definative answer for that. How causality works in quantum mechanics is still being debated, and how the universe in general works is still too much of a mystery to be able to ask such a broad question like that.

[alt_f13]

Personally, I would find it hard to believe that things could re-happen just the way they have, merely because the scale on which the seemingly random quantum disturbances happened is so much larger than the scale at which they happen now. I guess it comes down to if you believe in fate.

 

"Is it possible that there are no coincidences?" -Mel, Signs

[Martin]

... assuming all conditions were exactly as they were 14 billion years ago,...

 

no

 

when you assume "all conditions are exactly the same" you are assuming that the INITIAL WAVEFUNCTIONS of space geometry and matter are the same (at a given moment, like one second prior to the bounce or one nanosecond prior, or one femtosecond after the bounce, or whatever)

 

THAT DOESNT DETERMINE MACRO OUTCOMES like you at your keyboard.

 

We can assume for sake of argument that you can pin down the wavefunctions and prepare the system to be as it was the other time.

 

even if you prepare the system the same way and the wavefunctions evolve deterministically from go, it still does not guarantee particular outcomes.

============

 

anyway that's my take on it. maybe someone else will take a different stance.

 

quantum cosmology is not a cut and dried subject. it hasnt really been DONE. It has been tried. and there has been a little progress. but it is not complete.

standard Copenhagen quantum mechanics requires a separate OBSERVER who is outside the setup.

it was careless of Niels Bohr and those guys to set it up that way, because

it makes it very hard to do cosmology in a kosher quantum way since there is no observer outside the setup.

 

so for starters QM has to be reconstructed.

 

the cosmologist James Hartle has been giving talks about how we need to reconstruct QM to adapt it to the need of doing cosmology.

he is famous and an excellent speaker

for a Hartle talk go to

http://streamer.perimeterinstitute.ca:81/mediasite/viewer/FrontEnd/Front.aspx?&shouldResize=False

 

and hunt around in the menus. they have streaming video

 

he recently gave a seminar on it that is in their "seminar series"

menu on the upper left.

 

I don't mean the inaugural talk that hartle gave at Perimeter's grand opening, along with Roger Penrose etc. that is hoopla.

I mean the seminar talk about the need to rebuild quantum mechanics for cosmology sake

[gib65]

So what I'm hearing from you guys is, even among the hardnosed believers of quantum mechanics, there is no consensus on the matter?

 

Personally' date=' I would find it hard to believe that things could re-happen just the way they have, merely because the scale on which the seemingly random quantum disturbances happened is so much larger than the scale at which they happen now. I guess it comes down to if you believe in fate.

 

"Is it possible that there are no coincidences?" -Mel, Signs[/quote']

 

Oh, yes, I forgot to take this into account. Let me know if I've got this right. What you're saying is that, at the very early stages of the universe, the scale at which these qauntum phenomena occurred were much larger? If that's the case, then there's no telling how the universe would have turned out should it have started over.

[Severian]

I agree with Martin. Quantum Mechanics only allows predictability in large statistical samples. The wavefunction collapses would be different so we would end up with a different universe.

[Prime-Evil]

"assuming all conditions were exactly as they were 14 billion years ago"

 

Then the answer would be yes. Except that if all conditions were the same as 14 billion years ago, then it might actually have to be 14 billion years ago also, or would it? Not sure. It get's into the more metaphysical question of what causes the Big Bang, and whether that cause is part of the universe, or not. Hypothetically, if all the conditions that caused the universe were the same, then the universe would turn out the same. This also assumes that, by definition, there is no external intervention after the Big Bang. In my own way of thinking the Big Bang never actually occured at a distinct point in time. It exists as a theoretical point in time. Like absolute zero is a theoretical point in temperature, but not one that is actually achieved. Same with a perfect vacuum, and the speed of light, and the Big Freeze. The universe has a theoretical finite life span, but it never actually gets there.

 

Of course I am not certain of this. I would even say I have enough knowledge of this sort of physics to call it a theory, and I am not even sure I would call it a belief. Just a way of thinking that has evolved. Any one else think along these lines, or do you know of someone that does? There must be many ways to be wrong, huh? But only one way for me at this moment. Well, sometimes I am capable of having more than one idea in my head at once, and they can both be wrong.